Usually I don’t use a db cache for two reasons:
1. db caches are replacements of wordpress core functionalities as far as I know and a WordPress update can literally break the blog if the db cache is not fully aligned with (possible) database/library changes.
2. a normal cache, lite lite cache, hyper cache, w3total cache, wp super cache, after the first request of a page on subsequent requests does not let wordpress to activate the database connection so db cache is never hit.
Of course post-unrelated queries can be cached and used by a db cache, but being them used only on first page request how much benefit we can get?
Vice versa, a blog with many registered user which cannot benefit from the classic cache or blog with a classic cache that does not support natively comment-cookies (lite cache does) and a lot of reader which are commentators can have improvements by a db cache.
Stefano.
